Coote and Strayer 2009 - Polgar

8/10/2019 Coote and Strayer 2009 - Polgar

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GASTROPODS OF THE HUDSON RIVER SHORELINE: SUBTIDAL, INTERTIDAL,

AND UPLAND COMMUNITIES

A Final Report of the Tibor T. Polgar Fellowship

Thomas W. Coote

Dept. of Wildlife and Fisheries ConservationUniversity of Massachusetts-Amherst

Amherst, MA 01002

Project Advisor

Dr. Dave Strayer

Cary Institute of Ecosystem StudiesMillbrook, NY 12545

Coote, T. and D. Strayer. 2009. Gastropods of the Hudson River Shoreline: Subtidal,

Intertidal, and Upland Communities. Section IV: 32 pp.InS.H. Fernald, D. Yozzo and H.

Andreyko (eds.), Final Reports of the Tibor T. Polgar Fellowship Program, 2008. HudsonRiver Foundation.


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ABSTRACT

The tidal Hudson River shore zone is a unique and dynamic ecotone, supporting a

great abundance of wildlife and fulfilling numerous ecological roles, but simultaneously

subject to intense human activity. A survey was completed for gastropods inhabiting six

dominant shore zone types along the Hudson River, including natural and altered

shoreline structures: sand, bedrock, unconsolidated rock, riprap, sea wall and timber

cribbing. Each of these shore zone types was surveyed at three river sections, lower, mid

and upper, from Poughkeepsie to Albany. Three elevations were sampled at each site:

sub-tidal, inter-tidal and upland. Eighteen sites between Poughkeepsie and Albany were

sampled in June during two intensive trips, resulting in a total of 23 taxa of gastropods.

Of these, three were exotic, includingBithynia tentaculata, whichwas represented by

only one specimen, indicating a significant decline for this species since the mid-1980s.

Three aquatic species were new records for the Hudson River, including Floridobia

winkleyi, which was present in significant numbers, as well as the recently recorded

Littoridinops tenuipes, also present in large numbers. Another new record was the

presence of two specimens of the New York state listed snail Valvata lewisi. Two

landsnails, Pomatiopsis lapidariaand Vallonia costatawere also found below high tide.

ANOVAs examining abundance and diversity of gastropods by shore type, elevation andriver section, indicate that mid-river sites, in combination with riprap and unconsolidated

rock, at inter-tidal elevations, contain significantly higher abundances and diversity of

gastropods. Regression analysis indicated that fine-scale environmental variables such as

site slope, rugosity and complexity do not explain the abundance and diversity of

gastropods at this level of analysis. Additional analysis included NMS ordination and

qualitative analysis.


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TABLE OF CONTENTS

Abstract IV-2Table of Contents. IV-3

Lists of Figures and Tables.. IV-4

Introduction.. IV-5

Methods... IV-8

Site Protocols.. IV-8

Sample Processing IV-11

Analysis... IV-12

Results . IV-12

Qualitative IV-12

Quantitative.. IV-18

Discussion IV-25

Acknowledgments IV-28

Literature Cited. IV-29


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LIST OF FIGURES AND TABLES

Figure 1 Map of study site.. IV-9

Figure 2 Schematic of sample site.. IV-9

Figure 3 Selected photographs of snails. IV-14

Figure 4 Incidence of land snails collected in early versus late June. IV-17

Figure 5 NMS ordination of samples.. IV-24

Figure 6 NMS ordination of species... IV-24

Table 1 List of gastropods found in the Hudson River between 1867-2008. IV-16

Table 2 List of upland snails. IV-17

Table 3 3-way ANOVA table for log transformed snail abundance. IV-19

Table 4 Raw mean snail counts. IV-19

Table 5 3-way ANOVA table for species.. IV-20

Table 6 Raw mean species counts. IV-21

Table 7 Correlation table for slope (log10), rugosity, complexity,

abundance (log10), and H.. .. IV-23


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INTRODUCTION

The Hudson River is tidal for 248 kilometers from New York City to Troy. Its

shoreline is complex and dynamic, and like many ecotones, supports a very diverse

fauna. At the same time, the tidal shoreline is not well understood ecologically (Strayer

and Smith 2000) and the human impact on it is of great significance (Limburg and

Schmidt 1990). Large-river shorelines like the Hudson have sustained significant damage

to their original ecological functions by virtue of the destruction of wetlands, the

replacement of natural shoreline habitats with artificial and erosion-resistant riprap and

bulkheads, development and pollution. Moreover, they continue to support a great deal of

human activity through recreation, fishing, transportation and water withdrawals for

commercial, agricultural and urban needs (Daniels et. al. 2005). Shorelines at once serve

as the point of impact for many of these human activities, while simultaneously providing

significant ecological services as a dynamic interface between the aquatic and upland

communities.

One class of organisms common along shorelines is the gastropods (Jokinen

1992). There are at least 50 species of freshwater snails in the Hudson River Valley, of

which at least four are exotic (non-indigenous to North America), and another 4-6 may be

invasive (introduced from other North American regions) (Strayer 1987). In addition,

there are at least 85 species of land snails in New England (Nekola 2005), most of which

can be found in the Hudson Valley, though not necessarily on shore lines. Gastropods are

well known as being sensitive to ecological change, particularly sensitive to pollution,

and a substantial resource base for fish, crayfish, waterfowl and small mammals (Dillon


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2000, 2005). However, the understanding of the role of these invertebrates within the

multitude of habitats in which they exist is minimal.

Efforts to understand and conserve invertebrates was not a pressing issue for most

states until the mid 1980s, and the understanding of their ecological role remains weak

(McCollough 1997). Currently there are 23 snail species on New York States rare animal

list (NYSDEC 2008), and the status, trends and ecological needs of most of these species

are poorly known.

While invertebrates make up nearly 99% of all animal diversity, they have

received significantly less attention than vertebrates, with mollusks receiving even less

attention despite their being considered one of the most threatened groups of animals

(Lydeard et al. 2004). Between 1500-2008, 257 gastropods became extinct (37% of all

animal extinctions during that time) and the number of gastropods on the International

Union for Conservation of Nature Red List of Threatened Species in 2008 was 883

(IUCN 2008). Despite these numbers, less than 2% of known mollusk species have been

properly assessed (Lydeard et al. 2004). Given the general decline of snail species in the

United States, as well as the loss of habitat associated with that decline (Burch 1989;

Lydeard et al. 2004), the ecological importance of snails (Kabat and Hershler 1993), the

contribution of rare invertebrates to species richness in aquatic systems (Cao et al. 1998),

and the relative lack of knowledge of gastropods, there is a need to develop a greater

understanding of the gastropod communities in the Hudson River shore zone. This report

provides baseline data on shoreline gastropods, and contributes to the understanding of

gastropod communities along the Hudson River.


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This project is part of a larger study, theEcological Functions of Hudson River

Shorelines, being conducted by David Strayer and Stuart Findlay of the Cary Institute of

Ecosystem Studies in collaboration with the Hudson River National Estuarine Research

Reserve (HRNERR). One key objective of this broader study is to provide basic

information required for maintenance and restoration of the shore zone, and to articulate

the different functions of natural and engineered structures and ecological communities.

Operating within this framework, gastropods were examined across six shoreline types:

sand, unconsolidated rock, bedrock, riprap, timber cribbing and sea wall (revetment and

sheet pile). Two main questions were addressed: 1) is the abundance and diversity of

snails greater on complex habitats and diverse substrates, and 2) is the abundance and

diversity of snails associated with exposure to disturbance? Under the first hypothesis

habitats with greater diversity of plant cover, complexity of substrate and higher levels of

organic material would contain greater densities and higher diversity of snails (Lodge et.

al 1987, Thorp et. al 1997, Strayer and Smith 2000). Under the second hypothesis

increased exposure to wind, waves and human disturbance would result in lower numbers

of snails (Strayer and Smith 2000).

In addition to contributing to the understanding of the ecological importance of

gastropod communities in the shore zone, this study provides critical information for

understanding the impact of current and future alien species (Loo et. al. 2007), notably

the establishedBithinia tentaculata,the anticipated New Zealand Mud Snail

(Potamopyrgus antipodarum), and the recently discovered molluscivore, the Chinese

mitten crab (Eriocheir sinensis) (Schmidt 2008, pers. comm.). The full impact of

invasives remains unknown but continues as a significant concern (Mills et al. 1996).


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METHODS

Gastropod communities from three sections of the Hudson River (lower, mid,

upper), from Poughkeepsie to Albany (Fig. 1), were sampled across six shoreline types:

sand, unconsolidated rock, bedrock, riprap, timber cribbing and sea wall. For each of

these shoreline types data were collected on three elevation zones: subtidal, intertidal and

upland. Sampling took place during two overnight field trips in the early summer of

2008, the first taking place June 1st through the 3rd, and the second June 29th through

July 1st. Each site was identified using GPS coordinates provided by Dr. Strayer and

HRNERR.

Because of the variety of habitat structures found among the shoreline types and

elevations, a variety of sampling techniques were employed, using a 3x3 quadrat design

at each site (Fig. 2). The sub-tidal zone is that portion of the river bank that lies just

below low-tide level, the intertidal zone is that portion of the river bank that is cyclically

inundated with water as the tide rises and falls, and the upland zone is the shore bank

immediately above the high-tide mark. These three zones mark the dynamic interface

between the river and the surrounding landscape, with each providing different species

composition, habitat structure and function.

Site Protocols

Three different collection protocols were used to cover the three elevations at

each of the sites. These protocols combine quantitative plot sampling with full-site visual


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Figure 1. Map of the study area showing sample sites at each river section.

Figure 2. Illustration of site with sample quadrats and their relative position.

inspections to capture unusual habitats or species. For each of the 18 sites, three quadrats

along 100 meter transects were laid parallel to the shoreline for each elevation. Figure 2

shows an idealized quadrat arrangement, but it does not indicate the complexity of habitat

structures for a given site; thus, actual layout in the field was more complex. For

Upland

high-tide

Intertidal

low-tide

Subtidal


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example, sea wall sites were typically in deep water and therefore the idealized shore

profile did not exist. Regardless, in all cases this basic design was employed, sampling

parallel to the shoreline with each quadrat at least 10 meters apart.

In the sub-tidal zone, three 30-second sweeps of substrate were completed with a

1,200 m mesh D-net. Each sweep covered one-meter square, at one-meter depth below

mean low tide. The selection of sample plots was selected in-situ based on

appropriateness of habitat (e.g., inclusion of vegetation, exclusion of sharp rock substrate,

etc.). Due to low visibility, in most cases a priori determination of vegetation was not

possible, but vegetation was included in the sample whenever possible.

In the intertidal zone, three one-meter square plots were sampled at mid slope

(during low tide), using a combination of handpicking and a 1.4 mm sorting sieve.

Depending on substrate type, picking frequently included turning over of rocks, pulling

of submerged vegetation and the washing of sediments. In a few cases, snails were

exceptionally abundant in the inter-tidal zones. In these cases quadrats were divided into

either half or quarters and total numbers determined accordingly.

For the upland zone, sampling took place within 10 meters of the high tide mark.

This habitat was by far the most complicated, including multiple scaled structures and

micro-habitats. Selection of quadrats attempted to include as broad a range of habitats as

possible. Handpicking and a 6.6 mm and 1.4 mm sieve were used for sorting the detritus,

soil, and rocks. Sampling included the examination of large rocks, plants, and trees.

A number of abiotic response variables have been identified including: mean

slope, shoreline complexity, rugosity, sediment grain size, organic content, vegetation

structure, coarse woody debris, wrack, turbidity, peak wave energy and exposure (D.


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Strayer and S. Findlay, pers. comm.). Mean slope, complexity and rugosity are included

in analysis here. Slope was determined using two methods, first using a line level from 1

meter below low tide to 1 meter above high tide, and second, using a depth finder to

determine slope from the 1 meter point below low tide, to 5 meters perpendicular off

shore. Complexity was measured using 1 meter calipers and measuring the shoreline as it

ran parallel to the 100 meter straight measure, using the ratio of the length measured by

the calipers to the taut 100 meter line. Complexity equals 1 for a shoreline that runs

exactly parallel to the 100 meter line, or higher for shorelines that deviate from the 100

meter line. Rugosity is the vertical roughness of the shoreline substrate, and was

measured using a 1 meter chain lain as closely as possible to the substrate contours. The

covered distance is then measured by a taut tape, and a ratio determined for chain length

(1 meter) to the tape length.

Sample Processing

While all sub-tidal samples were collected with a dip net, the inter-tidal and

upland samples were typically handpicked or run through sieves to collect all snails

greater than 2 mm. All snails collected were preserved in full strength, 95% analytic

grade ethanol for later identification and possible genetic analysis (Dillon 2005). Snails

were identified in the lab to genus or species using standard references (Pilsbry 1939-

1948; Harman and Berg 1971; Burch 1962, 1989; Jokinen 1992). Voucher specimens will

be deposited at the National Museum of Natural History, Washington, D.C.


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Analysis

Because of the distinctive elevation community types (subtidal, intertidal, and

upland) and the different sampling techniques and conditions, statistical comparisons

across elevations should be viewed cautiously. Statistical analysis includes ANOVAs for

density (abundance) and diversity on elevation, shore type and river section, as well as

regression analysis for diversity and density against exposure, rugosity and slope. For

diversity, both species richness as well as Shannons diversity index (H) were used. Non-

metric multidimensional scaling (NMS) (McCune and Grace 2002) was also used to

assess differences in gastropod community composition across different types of

shorelines. Statistical analysis includes only the data collected as part of the primary 3x3

sampling design for each site as described above, and does not include data collected as

part of each site survey, or from additional sampling. These additional data are included

in qualitative analysis.

RESULTS

Qualitative Analysis

The diversity of aquatic gastropods collected in this project is consistent with

previous studies (Strayer 1987), representing 14 of the 30 taxa known from the river

(Table 1). In addition, three newly reported aquatic species in the Hudson were

documented in this study. Figure 3 includes pictures of the selected species discussed

below. Table 1 lists all reported historical records and covers dozens of separate studies

(Strayer 1987). Three of the species in Table 1 are known exotics, and four are suspected

invasives via the Erie Canal, of which one of each was collected in this study.Bithynia


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tentaculatais an exotic snail and is known to be an intermediate host for a number of

lethal waterfowl trematodes (Sauer et al. 2007). The suspected invasive is represented by

a single recently empty shell of Pleurocera acuta. No detrimental effects of this invasive

have been reported.

Live specimens of three previously unreported species for this section of the river

were also collected during this study. SeveralLittoridinops tenuipeswere found

throughout the lower and mid river study sites, and, although this species was reported

for the first time in the lower river in 2001 (Strayer & Smith 2001), this is their first

documented finding north of Poughkeepsie. Two individuals on the New York state list

of species of special concern, Valvata lewisi, and several Floridobia winkleyi, were also

found. It is important to note that the original identification of F. winkleyiin this study

wasMarstonia lustrica, a species previously reported from the river by a number of

researchers, and morphologically almost identical to F. winkleyi. After the original

identification, genetic analysis was completed on several specimens for the mitochondrial

gene COI (Liu pers. comm.). These results unequivocally identified these snails to be F.

winkleyi.No specimens ofM. lustricawere identified in this study. This first record of F.

winkleyiin the river, and in the state of New York, represents a significant shift in its

known range, with the only other records occurring in tidal coastal fresh and brackish

waters extending from Connecticut to Maine (Davis & Mazurkiewicz 1985; Smith 1994).


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Figure 3. Selected photographs of some snails found during this study. Clockwise starting from the top:

Littoridinops tenuipes, Pomatiopsis lapidaria, Floridobia winkleyi, Vallonia costata, and Valvata lewisi.

Scale bar is approximately 1.0 mm: -------------

Two upland species not previously reported in Hudson River surveys were

collected below the high-tide mark. Vallonia costatawas represented by one specimen,

and was found on bricks in timber cribbing in the inter-tidal elevation. Pomatiopsis


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lapidaria, known to be amphibious, was found at several sites in the mid and upper river

sections, was represented by several specimens, and was found both in the upland and

inter-tidal elevations. Due to its amphibious nature, P. lapidaria has rarely been reported

in New York (Strayer, pers. comm.), with only a handful of records. No specimens were

reported by Strayer (1987) or Harman and Berg (1971), and Jokinen only reported one

live population in her survey of New York (Jokinen 1992).

The results for land snails overall are disappointing. The upland elevations

yielded fewer species and lower numbers than what was expected (Table 2). The two

genera of slugs found, ArionidaeandDeroceras,are invasives, and are common

throughout the northeast United States. While sampling in the upland elevations at each

of the sites was extensive, it appears that relatively dry weather resulted in low incidence

during the primary upland sampling trip in early June. This is evident when comparing

the fifteen upland sites surveyed in early June to an additional three sites sampled in late

June (Figure 4), which followed rain events throughout the month. Due to logistical

constraints, additional sampling of the upland sites was not feasible.


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Prosobranch snails 1867-1900 1936 1972-1985 2008

Valvata lewisi xValvata piscinalis

1 x

Valvata sincera x

Valvata tricarinata x x x

Viviparus georgianus1 x x

Campeloma decisum x x

Lioplax subcarinata x x

Bithynia tentaculata1 x x x x

Probythinella lacustris x x x x

Gillia altilis x x

Birgella subglobosa2 x

Littoridinops tenuipes3 x

Marstonia lustrica x

Amnicola limosa x x x

Amnicola pupoidea x

Goniobasis (=Elimia) livescens2 x x x

Goniobasis (=Elimia) virginica x x x x

Pleurocera acuta2 x E

Floridobia winkleyi x

Pulmonate snails

Pseudosuccinea columella x

Lymnaeidae x x x x

Physidae(Physella) x x x x

Gyraulus deflectus x x

Gyraulus parvus x x x x

Helisoma anceps x x x

Micromenetus (Menetus) dilatetus x E

Planorbella trivolvis x x x

Promenetus exacuous x x x

Ferrissia rivularis x E

Laevapex fuscus x

Land snails found below high tide in 2008

Pomatiopsis lapidaria x

Vallonia costata x

Table 1. Historical survey results of gastropods in the Hudson Valley (Strayer 1987) combined with this

studys findings. (E=recent empty shells, 1=Exotic, 2=Suspected Invasive, 3=First reported in 2001(Strayer & Smith 2001))


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Upland Gastropods Abundance

Stenotrema hirsutum 1Euchemotrema fraternum 1

Deroceras sp.1 7

Arionidaesp.1 6Novisuccinea ovalis 21

Helicodiscus parallelus 1Retinella rhoadsi 1Vallonia costata2 2Pomatiopsis lapidaria2 13

Table 2. List of land snails found in this study. (1. exotic 2. inter-tidal)

0

50

100

150

200

250

300

350

400

total # ind. total # taxa

June 1-3 (N=15)

June 28- July 1

(N=3)

Figure. 4. Incidence of land snails in the beginning of June and the end of June. 15 upland sites were

surveyed from June 1-3 and 3 sites were sampled from June 28-July 1.


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Quantitative Analysis

The distribution of snail counts in the samples deviated significantly from normal

(Shapiro-Wilk= 0.29) and so the data were subjected to a log10transformation. Following

this transformation, the distribution of the data still deviated from normal, but less so

(Shapiro-Wilk= 0.78). Species richness distributed more closely to normal (Shapiro-Wilk

= 0.78) and log10transformation did not result in any improvement, so these data were

not transformed for analyses. The transformed snail count data were subjected to a 3-way

ANOVA, examining the effects of the three independent variables: elevation, shore type

and river section.

For abundance, the ANOVA revealed significant main effects of elevation, shore

type and river section (Table 3). Tukey post-hoc comparisons indicated that across shore

types, sand and sea wall contained significantly lower numbers of snails, while

unconsolidated and riprap contain significantly higher numbers. The mean snail

abundances are also higher in the lower and mid river sections than at the upper river

section. Post-hoc tests also indicated the highest snail count at the inter-tidal elevation, as

expected due to sampling efficiency.

All of these main effects were qualified, however, by a significant three-way

interaction (Table 3). Examination of the means across the 54 cells revealed higher snail

counts in the riprap and unconsolidated rock river sections, and highest at the intertidal

elevation (Table 4).


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ANOVA

total_snails_log10 Experimental Method

Sum ofSquares df Mean Square F Sig.

Main Effects (Combined) 40.805 9 4.534 23.893 .000

elevation 24.843 2 12.421 65.459 .000shore type 13.811 5 2.762 14.557 .000

river section 2.151 2 1.076 5.668 .005

2-Way Interactions (Combined) 24.730 24 1.030 5.430 .000

elevation * shore type 13.948 10 1.395 7.351 .000

elevation * river section 2.569 4 .642 3.389 .012

shore type * river section 8.212 10 .821 4.328 .000

3-Way Interactions levation * shore type * riverection

14.239 20 .712 3.752 .000

Model 79.774 53 1.505 7.932 .000

Residual 20.494 108 .190

Total 100.268 161 .623

Table 3. Three-way ANOVA summary table for log10transformed snail abundance.

Elevation upland intertidal subtidal

Riversection lower mid upper lower mid upper lower mid upper

bedrock 0.33 0.00 0.00 8.67 89.33 16.33 7.33 3.33 0.33

cribbing 2.00 0.00 0.33 23.67 184.00 23.00 0.00 1.33 2.33

unconsolidated 18.67 83.33 10.67 267.33 224.00 0.00 5.00 5.00 0.00

riprap 0.00 0.00 0.00 12.33 582.67 154.00 30.67 7.00 1.67

sand 1.33 5.00 2.00 0.00 0.00 3.67 0.00 4.00 2.33

seawall 0.00 0.00 0.00 0.00 0.00 98.00 0.00 0.67 0.00

Table 4. Raw mean snail counts by cell (cell ns = 3). Bold indicates significantly (p=.05) higher counts.

The ANOVA on the number of species (richness) indicated significant main

effects of elevation, shore type and river section (Table 5). Tukey post-hoc analysis

indicates that across shore types, sea wall contains significantly lower numbers than

riprap, unconsolidated rock and bedrock; across elevation, species richness was

significantly lower at the upland sites.


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These main effects were again qualified, however, by a significant three-way

interaction (Table 5). Examination of the mean total species counts across the 54 cells

again revealed higher counts in riprap and unconsolidated rock, and again at the

intertidal, but also sub-tidal, elevations (Table 6).

To test for possible effects of upland and subtidal elevations on the inter-tidal

elevation, an additional ANOVA was run on the inter-tidal elevation only. There was a

highly significant effect for shore type on total species richness, F (5,36) = 5.48, p


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Elevation upland intertidal subtidal

River section lower mid Upper lower mid Upper lower mid upper

Bedrock 0.33 0.00 0.00 2.67 3.33 1.00 2.33 1.33 0.33

Cribbing 1.33 0.00 0.33 0.67 2.67 1.33 0.00 1.00 1.00Unconsolidated 1.00 1.00 1.67 3.33 3.00 0.00 1.00 2.33 0.00

Riprap 0.00 0.00 0.00 1.67 3.00 2.33 3.00 2.67 1.00

Sand 1.00 1.33 1.67 0.00 0.00 0.67 0.00 1.00 1.33

Seawall 0.00 0.00 0.00 0.00 0.00 1.67 0.00 0.33 0.00

Table 6. Mean species counts (cell ns = 3). Bold indicates significantly (p=.05) higher species counts.

There was also a significant effect for shore type on log10abundance, F(5,36)=

14.53, p


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Correlation analysis for the three ordination axis for samples, along with slope,

rugosity, complexity, elevation, river section and shore type were completed (Figure 5).

The results indicate that 17.6% (r2) of axis one can be explained by slope, 20.1% can be

explained by rugosity, and 34.5% by elevation. For axis 2, only elevation has any

explanatory power accounting for 21.2% of the results, and for axis 3, elevation and river

section explain 19.8% and 14.8% of the data respectively. The clusters of species in

Figure 6 coincide with the clustering of samples in Figure 6, showing that the ordination

has grouped the data according to the dominant species for each sample. Despite low

numbers (less than 10 individuals), the upland species are clearly clustered together

where no other species occurred. Samples that were dominated by Physidae and

Lymnaeidae are clustered at the top of axis 3. F. winkleyiand P. lapidariaare clustered

with Physidae and Lymnaeidae because they are present in those same samples at

relatively high numbers. Of the 22 samples represented by the cluster of Physidae,

Lymnaeidae,F. winkleyiand P. lapidaria, 19 are inter-tidal, two are upland and three are

sub-tidal. Samples that were dominated byA. limosaandL. tenuipes, and had only one

or two individuals from other species, are clustered at the bottom of axis 1 and 2. Three

of these samples are inter-tidal and 16 are sub-tidal. Overall, the patterns of snail

occurrences are relatively weak, but do indicate that there is some effect of environmental

variables on the distribution of gastropods, particularly elevation.


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Table 7. Correlations between slope, complexity, and rugosity on H and snail abundances (N). Slope and

abundances were non-normal and subjected to log10transformation.

slope rugosity abundance complexity H

slope Pearson Correlation 1 .477 -.238 -.368 .179

Sig. (2-tailed) .045 .341 .133 .476

N 18 18 18 18 18

rugosity Pearson Correlation 1 -.461 -.098 .163

Sig. (2-tailed) .054 .698 .518

N 18 18 18 18

abundance Pearson Correlation 1 .435 .232

Sig. (2-tailed) .071 .354

N 18 18 18

complexity Pearson Correlation 1 .117

Sig. (2-tailed) .642

N 18 18

H Pearson Correlation 1

Sig. (2-tailed)

N 18


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Figure 5. NMS ordination of samples.

Figure 6. NMS ordination for species.


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DISCUSSION

The goal of this project was to survey gastropods across the six different shore

types, and to draw some conclusions on how the various assemblages correlated with the

various ecological and physical structures. It is clear from the analysis that the inter-tidal

elevations supported the majority of snails, although the data on the upland and sub-tidal

elevations are relatively weak. At the inter-tidal elevation, the unconsolidated rock and

riprap habitats supported the most snails and the most species, although bedrock also

supported a high number of species. Sand beaches and seawall structures were the most

depauperate.

Generally speaking this study suggests that stable, medium scale structure (brick,

small rock, timber cribbing) may be beneficial to gastropod communities, whereas

unstable, fine scale (sand and unconsolidated rock), or stable large smooth structures

(seawall and large exposed basalt surfaces) are not as supportive. An issue for

management of shorelines then may be not so much a question of natural versus man-

made, but rather which type of structure is best suited to protect the shoreline while

simultaneously promoting aquatic life.

The environmental variables tested in this paper did not provide explanatory

power for the gastropod communities. This agrees with field observations, specifically

that there are a plethora of microhabitats in each of the major shoreline types, precluding

any distinct larger-scale pattern from emerging. For example, within the timber cribbing

sites, the variability in habitat structure ranged from large smooth faced basalt, to small


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rough bricks, to the wood support structure, with each type of habitat supporting different

abundances and different species. This type of variability existed at most of the sites.

However, NMS ordination does support elevation as a potential selecting factor,

distinguishing samples dominated byL. tenuipesandA. limosaas occurring primarily in

sub-tidal elevations, as opposed to Physidae, Lymnaeidae, F. winkleyi, and P. lapidaria

as dominating inter-tidal elevations.

Table 1 highlights several interesting results. First is the incidence of the

relatively rare and state-listed snail Valvata lewisi, which has no previous record in the

Hudson Valley. In this study, two live individuals were collected from mid-river cribbing

habitat, in the sub-tidal elevation. There are only two records for this species in New

York, one from a ditch in Onondaga County, in the St. Lawrence River watershed, and

one from Oneida Lake in central New York (Jokinen 1992).

Floridobia winkleyiis one of the most surprising finds. This species is new to

New York State, and represents a substantial increase in its known range. It is of

particular interest because of its close similarity morphologically toMarstonia lustrica,

which has been recorded occasionally in the Hudson River, but was not found during this

survey. The identification of F. winkleyicame about after initial identification asM.

lustricabased on morphology. Several specimens were then submitted for genetic

analysis as part of another project onM. lustrica, with the surprising result that they were

F. winkleyi.Further work needs to be completed to check historical lots and records to

determine if F. winkleyiis indeed new to the river, or if it has been mistakenly identified

asM. lustrica, or if both species are present andM. lustrica was simply not found during

this survey.


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Another species only recently reported for the upper Hudson River is

Littoridinops tenuipes. It is generally considered an Atlantic seaboard species, extending

from Florida to the northeastern shore of Massachusetts, with records only for the lower

Hudson River (below Poughkeepsie) (Smith 1987; Strayer pers. comm). This species was

a common occurrence throughout the lower and mid-river sections in this study (both

above Poughkeepsie), but was not represented in the upper river section. It is possible

that this species is a relatively recent introduction to the river and is moving upstream.

Pomatiopsis lapidariais a species that is also considered rare in New York, yet it

occurred at four locations, in all three river sections. The land snail Vallonia costatawas

found attached to bricks in timber cribbing in the inter-tidal elevation, raising the

possibility that it is amphibious. Only one specimen of the exoticBithynia tentaculata

was found, which is in stark contrast to Strayers (1987) findings in 1985 when they

covered the rocks of the inter-tidal zone of the shoreline. While this study is not

conclusive, it does appear that this species has declined significantly.

The results of this project highlight the great variety of habitats and community

structures, and variety of gastropods that inhabit those environments, the multiple scales

of interest, and the dynamic nature of the Hudson River shoreline. It also highlights how

little is understood about gastropods and their relationship to the environment, while

highlighting that such understanding is not beyond grasp, and that this information is

critical for appropriate management. Recommendations for further study include

repeating the work attempted here in the upland elevations, as well as looking closer at

the potential differentiation of species occurrence in the inter-tidal and sub-tidal

elevations.


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ACKNOWLEDGEMENTS

I would like to thank the Hudson River Foundation for their support through the

Polgar Fellowship, as well as Bard College at Simons Rock for their support through the

use of facilities and equipment. Ken Geremia and Ryan Bazinet helped make the

fieldwork possible and successful, and Kathy Schmidt played a critical role in the

identification of the upland species, for which I am indebted. I am also indebted to Anne

ODwyer from Bard College at Simons Rock for many hours of number crunching and

statistical analysis. Stuart Findlay and Dave Strayer both played a key role in the original

conception of this project and provided key information and data from their own study. I

would like to thank Dave Strayer for his generous support and assistance throughout the

study, and in particular for his help with identification of gastropods, and the use of his

lab at the Cary Institute.


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